The mouse zona pellucida is an extracellular glycocalyx comprised of three sulfated glycoproteins (ZP1, ZP2 and ZP3) which surrounds growing oocytes, ovulated eggs and dividing embryos. One of the proteins, ZP3, has been shown to be the primary sperm receptor and to induce the sperm acrosome reaction. The ZP3 gene is transcribed uniquely in oocytes and transcripts accumulate during the narrow two-week growth phase of oogenesis. We have determined that ZP3 is s single copy gene composed of 8 exons (ranging in size from 92- 338 bp) which encompass approximately 8.6 kg of DNA on mouse chromosome 6. We have identified a novel tandem repeat with a unit length of 54 bp which is re-iterated 6 fold, 500 bp upstream of the transcription start site. Studies are currently underway to determine if this repeat or other 5' flanking sequences play a role in the oocyte-specific, developmentally regulated expression of ZP3. The poly-adenylate ZP3 transcript contains short 5' and 3' untranslated regions and a single open reading frame sufficient to code for a core protein of 46,307 daltons. The cleavage of a putative 22 amino acid signal peptide would result in the secretion of a mature core protein of 43,943 daltons. One strategy to Investigate the biological functions of ZP3 is to examine the effect of anti-ZP3 antibodies on oogenesis and early development. We have described an anti-ZP3 monoclonal antibody that is effective in inhibiting in vitro and in vivo fertilization, but has no other effect on oogenesis or early development. This contraceptive effect is long-term (>15 estrus cycles), but eventually reversible. The epitope recognized by this contraceptive antibody has been identified by recombinant DNA techniques as a seven amino acid peptide. Mice vaccinated with this peptide produce antibodies which bind to endogenous intra-ovarian oocytes and the biological effect of these antibodies in mice is now being Investigated. Because the ZP3 gene is conserved from mouse to man, this contraceptive strategy may be widely applicable among mammals.